Multispeed hydraulic or pneumatic device

ABSTRACT

A hydraulic or pneumatic device with a cylinder and piston system provides a rapid stroke and a power stroke. The piston part of the system consists of two lengthwise integrally connected piston-rod like plunger pistons, with different diameters. The cylinder is also provided with two working chambers, one for each piston, each working chamber at least partly surrounding its own piston. In each the pistons there is a passage connecting the two working chambers.

United States Patent 1 91 I Bryntse et a1.

1451 July 23, 1974 MULTISPEED HYDRAULIC OR PNEUMATIC DEVICE [75] Inventors: Anders Ivar Bryntse, Mjolby; Karl Erik Berkestad, Linkoping, both of Sweden [73] Assignee: AB Bygg-och Transportekonomi (BI), Mjolby, Sweden 22 Filed; Mar. 16, 1973 21 Appl. No.: 342,217

[30] Foreign Application Priority Data Mar. 24, 1972 Sweden....'..... 3859/72 [52] US. Cl 91/411 A, 911/412, 92/110, v 92/152, 60/97 H [51] Int. Cl. FlSb 11/16 [58] Field of Search 91/411 A, 412, 441, 222; 92/109, 110, 152; 60/97 H, 477

[56] References Cited UNITED STATES PATENTS 2,049,335 7/1936 Stephens"; 60/97 H LIX 2,284,228 5/1942 Page 60/97 H x 2,532,735 12/1950 Sedgwick 91 441 x 3,134,232 5/1964 Barosko 91 412 X FOREIGN PATENTS OR APPLICATIONS 338,099 6/1959' Switzerland 91 441 Primary ExaminerEdgar W. Geoghegan Attorney, Agent, or Firm-Alter Weiss Whitesel &

Laff

' '57 ABSTRACT A hydraulic or pneumatic device with a cylinder and piston system provides a rapid stroke and a power stroke. The piston part of the system consists of two lengthwise integrally connected piston-rod like plunger pistons, with different diameters. The cylinder is also provided with two working chambers, onefor each piston, each working chamber at least partly surrounding its own piston. In each the pistons there is a passage connecting the two working chambers.

7 Claims, '1 Drawing Figure A 1 MULTISPEEDHYDRAULIC R PNEUMATIC D vrcE The present invention relates to a hydraulic or pneumatic device including a cylinder and piston system for providing a rapid stroke'and a power stroke. The device is especially although not exclusively intended for use in trucks for handling ofgoods,'e.g. pallet trucks.

Known pallet'trucks often have a fixed ratio between the movement of the pump piston and the movement of the lift piston. The ratio is so choosen that, with maximum load onthe pallet truck, it is possible manually to effect the movements of the pump piston via a lever system. The ratio is, therefore, not so effective when lifting light loads or when the truck is unloaded. The unloaded condition occurs after the pallettruck is inserted under the load and before it has been pumped up into engagement with the load. The height of this unloaded lift movement is dependent upon the shape of the pallet and usually varies between and 45 mm. A ratio often used in pallet trucks is so choosen that one pump stroke gives about 10 mm movement of the lift piston.

The main object of the present invention is to provide a movement of the lift piston, which movement is automatically'dependent on load, thereby eliminating most of the disadvantage mentioned above.

The basic conception of the present invention invoices a cylinder together with the lift piston wherein two effective pistons of different diameter are formed in working chambers. This two vdiameter'system provides lift forces almost everywhere along the whole length of the cylinder. Furthermore the construction is simple and economical and has a minimum number of movable parts. The method is especially suitable for cylinders having'a relatively short lengthof stroke, e.g. cylinders in pallet trucks. According to the invention, the piston and cylinder have outer dimensions in full conformity with conventional, well tested and well motivated structures.

According to the invention, there are in the cylinder,

displaceably mounted lengthwise two integrally con-' nected piston-rod like plunger-pistons, having these two pistons have different diameters. Each piston isat least partly peripherically surrounded by its own working chamber in the cylinder.

A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawing, which in a longitudinal crosssectional view'which shows the cylinder, according to the invention. Y

In the drawing, a cylinder housing 1 includestwo integrally connected, longitudinally aligned I piston-rod like plunger pistons 5 and 6'. These pistons have different diameters, of which the leading plunger piston 5 is the largest. The pistons 5 and 6 are practically sealed and guided in relation to the cylinder housing 1 by means of guides 3 and 4, and are arranged to run easily therein. The lengths of the pistons 5 and 6 are such that, when the pistons are fully extended, they must still be guided by the guides 3 and 4. The pistons 5 and 6 are further provided with a central bore 7, which together with passages 8 and 10, a ball 11, a valve seat 12 and a valve bore l3enables the pressure transmission medium (such as hydraulic fluid, for example) to pass from a first working chamber 14 to another longitudinally aligned working chamber 15, but not in the opposite direction, since the ball 11 is then sealed against the seat 12. The leading piston 5 works in chamber 15 and the trailing piston 6 works in chamber 14.

. The cylinder housing 1 also contains a reservoir 16 for the pressure transmission medium. Passages 17 and 18 enable the-flowof pressure transmission medium fromthe reservoir 16 to the working chamber 14, but not in the opposite direction, since a valve ball 19 is then sealed against a seat 20.

The'cylinder housing contains a further passage 21. A known valve system (not disclosed here) can be connected to a pump during the pumping up and to the reservoir during the lowering.

Furthermore the cylinder housing 1 contains a change over device in the form of a bore 29 and a valve comprising a hole 22, a ball-23, a piston 24, an O-ring 25, a spring 26' and a screw plug 27, provided with a hole 28. The piston 24 with the O-ring 25 is easily movable in relation to the bore 29. When the spring loaded valve'is opened, the passage 21 is connected to the working chamber 14 viathe hole 22, the ball 23 and a passage 30.

The .operation of the above described piston arrangement is as follows:

In order to extend the pistons 5 and 6, the pressure transmission medium is pumped, via the valve system known per se, through the passage 21 and into the working chamber 15-and through the passages 8 and 10 into the bore 7, the ball 11 thereby, being sealingly pressed-against the'seat 12. The communication between the passage 21 and the working chamber 14 is closed by the ball 23, which the spring 26 acting via the piston 24 sealingly presses against the opening of the hole 22. This means that the pressure of the medium acts only on the area, which corresponds to the difference between the diameters of the pistons 5 and 6. Therefore these pistons will make a large movement in relation to the quantity of pressure medium supplied. Pressure medium willalso be drawn from the reservoir 16 through the passage 17, past the ball 19 and via the passage 18 into the working chamber 14.

A If the pistons 5 and 6 are loaded so much, that the pressure of the medium arrives at a value whereby the total power acting in the sectional area of the hole 22 exceeds the spring power 26, then the ball 23 is pressed from its seat. The pressure medium then has free access to the working chamber 14 via the bore 29, the piston 24, and the passage leading into the working chamber 14. The ball l9'is now forced against its seat 20 to prevent the medium from flowing into the reservoir 16. The pressure of the medium is then immediately decreased to a value, which corresponds to the load of the piston 5 divided by the sectional area of that piston.

The screw plug 27 is provided with thehole 28 in order to ensure, that atmospheric pressure always exists on the surface of the piston 24 which faces the spring 26. i

The above described change-over device may comprise other means than the described valve 23 29, e.g.

through a small slot or the like, the pressure equalizing being made at a certain piston-rod load and pump speed. Such a system, however, is dependent upon the viscosity of the pressure medium and causes losses through the choke which the slot represents. By way of comparison, the change-over valve 23 29 is n0nsensitive to viscosity differences and can be substantially loss free.

In order to lower thepistons 5 and 6, the passage 21 is connected via the valve system known per se to the reservoir 16, in which there is substantially atmospheric pressure. This means that the medium in the working chamber 15 which'is over-pressure can freely flow to the reservoir 16, the medium in the working chamber 14 also being able to flow to the reservoir 16 through the valve bore 13, past the ball 11, the bore 7, the passages 8 and 10, the working chamber 15 and the passage '21.

The cylinder can be driven with either gas or liquid as pressure medium. I

We claim:

1. A lifting device operated by a hydraulic or pneumatic pressure transmission medium, said device comprising a piston and cylinder system for providing both a rapid stroke and a power stroke, acting in the same unidirection, the piston part of said system comprising two integral longitudinally aligned plunger pistons, the leading (with respect to the lifting direction) one of said plunger pistons having a larger diameter than the trailing one of said plunger pistons so that an annular shoulder is formed between the two pistons, said shoulder comprising a first pressure area acted upon by the pressure transmission medium, the trailing one of the pistons having another pressure area acted upon by the same medium, two separate and longitudinally aligned working chambers, formed in said cylinder-part of the system, the first of said working chambers containing said first pressure area and the second of said working chambers containing the other pressure area, means associated with each of said working chambers for supplying said pressure transmission medium thereto, valve means controlled by the pressure transmission medium comprising a pressure medium passageway formed in said pistons and connecting the two working chambers with each other, and means inserted in said passageway in said pistons to enable said pressure medium-to flow between said working chambers in only one direction.

2. The device of claim 1 and means for normallydirecting said pressure transmissionmedium into said first of said working chambers to act upon said first pressure area.

3. The device of claim 2 and second valve means for diverting at least a part of said pressure transmission medium from said first working chamber and into the second of said working chambers where said pressure transmission medium acts upon said other pressure area.

. 4. The device of claim 3 and means whereby said second valve means is operated responsive to pressure differentials when the pressure in the first working chamber exceeds the pressure in the second valve means by at least a predetermined amount.

5. The device of claim 4 wherein the relative dimensions of said working chambers and pressure areas are such that said plunger piston has an initial rapid stroke before operation of said second valve means followed by a power stroke after operation of said second valve means.

6. The device of claim 1 and means responsive to the pressure in the first working chamber exceeding the pressure in the second valve means by at least a predetermined amount for diverting at,least a part of said pressure transmission medium from said first working chamber and into the second of said working chambers where it acts upon said other pressure area.

. 7. The device of claim 6 wherein the relative dimensions of said working chambers and pressure areas are such that said plunger piston has an initial rapid stroke before operation of said second valve means, followed by a power stroke after operation of said second valve means. 

1. A lifting device operated by a hydraulic or pneumatic pressure transmission medium, said device comprising a piston and cylinder system for providing both a rapid stroke and a power stroke, acting in the same unidirection, the piston part of said system comprising two integral longitudinally aligned plunger pistons, the leading (with respect to the lifting direction) one of said plunger pistons having a larger diameter than the trailing one of said plunger pistons so that an annular shoulder is formed between the two pistons, said shoulder comprising a first pressure area acted upon by the pressure transmission medium, the trailing one of the pistons having another pressure area acted upon by the same medium, two separate and longitudinally aligned working chambers, formed in said cylinderpart of the system, the first of said working chambers containing said first pressure area and the second of said working chambers containing the other pressure area, means associated with each of said working chambers for supplying said pressure transmission medium thereto, valve means controlled by the pressure transmission medium comprising a pressure medium passageway formed in said pistons and connecting the two working chambers with each other, and means inserted in said passageway in said pistons to enable said pressure medium to flow between said working chambers in only one direction.
 2. The device of claim 1 and means for normally directing said pressure transmission medium into said first of said working chambers to act upon said first pressure area.
 3. The device of claim 2 and second valve means for diverting at least a part of said pressure transmission medium from said first working chamber and into the second of said working chambers where said pressure transmission medium acts upon said other pressure area.
 4. The device of claim 3 and means whereby said second valve means is operated responsive to pressure differentials when the pressure in the first working chamber exceeds the pressure in the second valve means by at least a predetermined amount.
 5. The device of claim 4 wherein the relative dimensions of said working chambers and pressure areas are such that said plunger piston has an initial rapid stroke before operation of said second valve means followed by a power stroke after operation of said second valve means.
 6. The device of claim 1 and means responsive to the pressure in the first working chamber exceeding the pressure in the second valve means by at least a predetermined amount for diverting at least a part of said pressure transmission medium from said first working chamber and into the second of said working chambers where it acts upon said other pressure area.
 7. The device of claim 6 wherein the relative dimensions of said working chambers and pressure areas are such that said plunger piston has an initial rapid stroke before operation of said second valve means, followed by a power stroke after operation of said second valve means. 